PM10 data were obtained from the relevant state bodies: the Department of
Environment, Climate Change and Water for Sydney; the Environment Protection
Authority Victoria for Melbourne; and the Department of Environment and
Resource Management for Brisbane. For each city 24-h average PM10 concentrations
were available for a network of monitors. To obtain an “overall” 24-h average PM10
concentration we took a simple average of the concentrations available on any
particular day. Similar to the procedure used in the National Morbidity, Mortality,
and Air Pollution Study (NMMAPS) we de-trended the PM10 concentrations from
each monitor before averaging across monitors (IHAPSS, 2005). We note that our
results are robust to whether or not the data were de-trended. In addition to PM10,
we obtained a daily measure of visibility measured using nephelometry, denoted
NEPH. NEPH measures light scattering by fine particles in the air between 0.1 and
2 mm in diameter (Morgan et al., 1998). We will use the NEPH concentrations to
provide a robustness check on the results for PM10.